Wrangler 2dr I made a mistake - Decatted JK.





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  1. #1
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    Default I made a mistake - Decatted JK.

    Hi guys

    Would appreciate your input.

    The catalytic converters were toast on my 2013 3.6 JK - rattling on acceleration. Instead of 40k for new cats, I took it in for a decat (minicats etc installed.)
    Jeep runs great, although my regrets as follows:


    • It's louder than I'd like, especially on cold start.
    • Sounds 'tinnier' - think E46 M3.
    • It stinks! When windows are open all I smell is carbon monoxide.


    How can I fix this aside from installing new units?
    Any exhaust shops recommended out in the Vale?
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  2. #2
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    Default Re: I made a mistake - Decatted JK.

    Quote Originally Posted by JasonRSA View Post
    Hi guys

    Would appreciate your input.

    The catalytic converters were toast on my 2013 3.6 JK - rattling on acceleration. Instead of 40k for new cats, I took it in for a decat (minicats etc installed.)
    Jeep runs great, although my regrets as follows:


    • It's louder than I'd like, especially on cold start.
    • Sounds 'tinnier' - think E46 M3.
    • It stinks! When windows are open all I smell is carbon monoxide.


    How can I fix this aside from installing new units?
    Any exhaust shops recommended out in the Vale?

    Off topic sorry but I love the way a stock E46 M3 sounds! That is a thing of beauty.
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  4. #3
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    Default Re: I made a mistake - Decatted JK.

    Quote Originally Posted by Willis View Post
    Off topic sorry but I love the way a stock E46 M3 sounds! That is a thing of beauty.

    Agreed! Sounds great - but not when you're rolling past the Spar in a muddy Jeep!

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  6. #4
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    Default Re: I made a mistake - Decatted JK.

    maybe chat to exhaust shop about adding another silencer to the system. Your are still stock on the exhaust, then add or replace with larger if possible

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    Default Re: I made a mistake - Decatted JK.

    Quote Originally Posted by JasonRSA View Post
    Agreed! Sounds great - but not when you're rolling past the Spar in a muddy Jeep!

    I agree! I wanted to upgrade my lexus exhaust because it has no sound really and that beauty of a V6 should be heard but im scared I mess that up.

    I think as someone has mentioned, try chatting to an exhaust place and see if they can add another silencer / muffler to help reduce the noise.

    No need to scare the old tannies when you driving past the shops for milk!
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    Default Re: I made a mistake - Decatted JK.

    Quote Originally Posted by Dwayne P View Post
    maybe chat to exhaust shop about adding another silencer to the system. Your are still stock on the exhaust, then add or replace with larger if possible
    Good advice. Add extra box(es). The larger the box the less and deeper sound. The further back the box the effect on sound is more.
    An offset box also has more noise dampening effect.
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    Default Re: I made a mistake - Decatted JK.

    also adding does not do harm N/A motors, back pressure does not cause worse performance, unlike the turbo and turbo diesel counterparts where it is better to get rid of warm gassed etc asap.

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    Default Re: I made a mistake - Decatted JK.

    Quote Originally Posted by Dwayne P View Post
    also adding does not do harm N/A motors, back pressure does not cause worse performance, unlike the turbo and turbo diesel counterparts where it is better to get rid of warm gassed etc asap.
    I suspect your definition on backpressure on a NA engine is not entirely correct. Back pressure on a NA engine is meant to be a negative pressure at the exhaust port. Adding silencers lowers the negative pressure, with loss of performance. The correct backpressure is obtained by calibrated branches and the correct size exhaust pipe, to optimise gas flow through the system to scavenge exhaust gasses from the ports and to minimise detonation of unburnt gas in the pipe.
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    Default Re: I made a mistake - Decatted JK.

    I think we need a video or sound clip!

    Did it make any difference to the fuel consumption?

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    Default Re: I made a mistake - Decatted JK.

    Quote Originally Posted by JasonRSA View Post
    Hi guys

    Would appreciate your input.

    The catalytic converters were toast on my 2013 3.6 JK - rattling on acceleration. Instead of 40k for new cats, I took it in for a decat (minicats etc installed.)
    Jeep runs great, although my regrets as follows:


    • It's louder than I'd like, especially on cold start.
    • Sounds 'tinnier' - think E46 M3.
    • It stinks! When windows are open all I smell is carbon monoxide.


    How can I fix this aside from installing new units?
    Any exhaust shops recommended out in the Vale?
    carbon monoxide is odourless.
    if it stinks, i would think you're smelling sulphur (hydrogen sulphide)

  17. #11
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    Default Re: I made a mistake - Decatted JK.

    Quote Originally Posted by JasonRSA View Post
    Hi guys
    The catalytic converters were toast on my 2013 3.6 JK - rattling on acceleration. Instead of 40k for new cats, I took it in for a decat (minicats etc installed.)

    Jeep runs great, although my regrets as follows:

    • It's louder than I'd like, especially on cold start.
    • Sounds 'tinnier' - think E46 M3.
    • It stinks! When windows are open all I smell is carbon monoxide.


    How can I fix this aside from installing new units?
    Any exhaust shops recommended out in the Vale?
    So, the only thing that you changed was the full CATs for mini- or fast CATs?

    It could be running great due to slightly less back pressure, but still sufficient for a NA. If you were replacing your headers, I'd look the anti-reversion style slightly smaller than the port size.

    * Yes, fast CATs are not as restrictive and thus, louder.
    * OEMs work hard at getting their models to sound a certain way. You have changed that. You could add an absorptive style of silencer to reduce high frequencies (tinny) without changing the back pressure significantly. Offset absorptive silencers are even quieter with a slight bit more loss of flow.
    * Have your fabricator turn the tailpipe down and away from the vehicle.
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  19. #12
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    Default Re: I made a mistake - Decatted JK.

    Apologies for the delay gentts.


    Here's a video - not entirely convincingly terrible.

    Fuel consumption... i'm bad at sums.

    The exhaust gasses may be coming in through the tailgate. It does let dust in when off roading.

    The smell is annoying/dangerous. Only when I have the windows down, and it lingers around the vehicle. Unless it's everyone around me!




    Quote Originally Posted by Dirk View Post
    I think we need a video or sound clip!

    Did it make any difference to the fuel consumption?
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    Default Re: I made a mistake - Decatted JK.

    The middle cylinder box is a resonator and the rear box is a muffler.
    I think in your case you could change the muffler and improve the exhaust sound. I've got a Magaflow axleback on my JKU which sounds great. But I haven't touched the cats.

    As for the exhaust fumes I'd say there is a leak somewhere. Something hasn't been sealed properly. I seem to remember a test one can do with light or gas to pick up leaks.

    See this Landrover thread as well
    https://www.4x4community.co.za/forum...-cat-now-smell
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  22. #14
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    Default Re: I made a mistake - Decatted JK.

    Quote Originally Posted by JasonRSA View Post
    Apologies for the delay gentts.
    Here's a video - not entirely convincingly terrible.

    ...The exhaust gasses may be coming in through the tailgate. It does let dust in when off roading.

    The smell is annoying/dangerous. Only when I have the windows down, and it lingers around the vehicle. Unless it's everyone around me!
    Do you have a drone in the cabin at certain rpm? From the clip, it sounds like that could be possible.

    I'd seal the tailgate starting with replacing the seals. You can thread a long rubber tube through some seals for an even better fit. I added sound proofing to the back side of the doors (so that it couldn't been seen from outside). My road noise and dust went down dramatically thereafter.

    Remove the CATs and the smell goes up, especially in a diesel. CATs also catch a lot of exhaust noise, but they are very flow restrictive.
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    Default Re: I made a mistake - Decatted JK.

    An update:

    I've grown accustomed to the 'new' noise. Not that bad.
    The fumes are annoying - with windows down exhaust gases come in via the vents behind the spare wheel.
    With windows up the problem goes away.

    However with soft top down, all windows down it does linger.

    I've since tried ordering replacement cats from Rock Auto - about $600 (R10,000) including shipping, ex taxes and duties. A big saving on the R40 odd thousand from local dealer.

    Two different payment attempts failed (CC and Paypal), after which my credit card was hammered by several ClickFunne* Trial Over charges for a similar amount.

    Looking into it and will revert.
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  24. #16
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    Default Re: I made a mistake - Decatted JK.

    Quote Originally Posted by JasonRSA View Post
    An update:

    The fumes are annoying - with windows down exhaust gases come in via the vents behind the spare wheel.
    With windows up the problem goes away.

    However with soft top down, all windows down it does linger.
    Convertibles have been around longer than catalytic converters.

    I'd fix the leaks as they contain deadly carbon monoxide. Just because you can't smell the fumes doesn't mean that you can't get asphyxiated.

    You can restrict the tip to increase the flow which must be pointed down and away from the vehicle so that you don't die when backing up. N/A loves restricted exhausts. Turbo engines can stack the charge the length of the system during hard acceleration and release during normal load conditions.
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  25. #17
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    Default Re: I made a mistake - Decatted JK.

    Jason my best advice would be to take it to a proper exhaust shop get them to sort it out it will be much cheaper than new cats!
    get a complete stainless exhaust roughly around R10k with the right mufflers, high flow cat and silencers!
    I will send you a few guys in a pm!

    To replace the stock cat is not necessarily going to solve your problem, it might be that the guys that removed it did a bad job
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    Default Re: I made a mistake - Decatted JK.

    Quote Originally Posted by HansieK View Post
    Jason my best advice would be to take it to a proper exhaust shop get them to sort it out it will be much cheaper than new cats!
    get a complete stainless exhaust roughly around R10k with the right mufflers, high flow cat and silencers!
    I will send you a few guys in a pm!

    To replace the stock cat is not necessarily going to solve your problem, it might be that the guys that removed it did a bad job
    this is the best advice and based on the original post, spot on

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    Default Re: I made a mistake - Decatted JK.

    @HansieK Thanks for the great info! Will definitely check it out.

    @jelo It was a considered and expensive exercise, performed by a reputable indie. Although I do enjoy the thought of you filing yet another throwaway chirp in your crack, alongside all the others.
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